KR920006928B1 - Liquid crystal display device - Google Patents

Abstract

No content.

Description

Liquid crystal display device

1 is a cross-sectional view showing the basic cell structure of a two-layer liquid crystal display device of the present invention.

2A and 2B are diagrams showing twists of liquid crystal molecules in left and right directions, respectively.

3 is a characteristic curve showing the relationship between the Δn ₂ · d ₂ and the transmittance of the second cell when the polarizer is positioned cross-nicotine in the liquid crystal display device of the present invention.

4 is a characteristic curve showing the relationship between the twist angle of the liquid crystal molecules and the contrast ratio of the display image,

5 is a characteristic curve showing the relationship between applied voltage and transmittance in a two-layer LCD.

6 is a cross-sectional view showing another liquid crystal display device (eg, two-layer TN-LCD) of the present invention,

FIG. 7A is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the display device of FIG. 6 of the present invention.

FIG. 7B is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the multilayer TN-LCD.

8 is a cross-sectional view showing another liquid crystal display device (e.g., two-layer SBE-LCD) of the present invention,

FIG. 9A is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the tomographic SBE-LCD. FIG.

FIG. 9B is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the display device of FIG. 8 of the present invention.

10 is a cross-sectional view showing another liquid crystal display device (eg, two-layer SEB-LCD) of the present invention,

FIG. 11A is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the tomographic SBE-LCD.

FIG. 11B is a characteristic curve showing the relationship between the applied voltage and the light transmittance in the display device of FIG. 10 of the present invention.

* Explanation of symbols for main parts of the drawings

C ₁ : first cell layer C ₂ : second cell layer

1, 13, 23: transparent substrate 2, 12, 22: transparent conductive film

3, 16, 26: alignment film 4, 15, 25: liquid crystal layer

6, 14, 24: sealing material 5, 11, 21: polarizer

32: electrode

The present invention relates to a multi-layer liquid crystal display device using a torsional nematic display method capable of obtaining an excellent color display.

Liquid crystal display devices are used today for a variety of applications in watches, electronic calculators and computer terminals, word processor displays, televisions and many other fields. In recent years, since the liquid crystal display device is changing to a multi-color and full-color display, the demand for this device is greatly increasing, and has already been put into practical use in the field of graphic display and image display. Actually widely used color displays are obtained by liquid crystal cells having a color filter layer. Since the liquid crystal cell acts as a light-converter, it displays various colors. The main type of display mode is a torsional nematic display mode in which the liquid crystal molecules are twisted at 90 ° so as to obtain high contrast and the like. However, in this TN display mode, it is impossible to achieve uniform switching of light over the entire spectrum of visible light because of the large dependence of the display characteristics on the wavelength of light. In particular, in the normal cloth display system in which the absorption axes of two polarizers exist in parallel, there is a problem that the color becomes dark due to light leakage when voltage is applied.

There are two main driving methods in a color display device which causes light-switching by the use of a TN display having this kind of color filter layer. One of these methods is an active-matrix driving method using a liquid crystal cell having a nonlinear device such as a diode or an image element having a switching element such as a thin film transistor, and the other method is to liquid crystal in a liquid crystal cell in the absence of the image element. It is a dual drive method that drives continuously. In the latter method, the inclination near the threshold of the optical characteristics of the liquid crystal is important, which is a problem in the TN display currently used. In order to improve the optical properties so that the inclination in the vicinity of the threshold can be obtained, a super-torsion birefringence effect (SBE) is proposed which imparts liquid crystal molecules twisted at approximately 180 to 270 degrees. In the SBE method, when the curve near the threshold increases sharply and the impact ratio is increased, a high contrast ratio can be obtained. However, since it uses the birefringent effect of liquid crystals, the dependence of the display characteristics on the wavelength is theoretically higher than that of TN displays. It is therefore very difficult to apply it for use in full-color displays.

The liquid crystal display device of the present invention, which solves the above-mentioned disadvantages and drawbacks of the prior art, has a two-layer liquid crystal cell composed of a first cell layer and a second cell layer, and a first cell layer containing liquid crystal molecules having a torsional nematic orientation. And a voltage applying means in one of the second cell layers, wherein the twist angle of the liquid crystal molecules in the first cell layer is opposite to the twist angle of the liquid crystal molecules in the second cell layer, and the liquid crystal molecules in the first cell layer near the second cell layer Orthogonal to the orientation of the liquid crystal molecules in the second cell layer near the cell layer.

In a preferred embodiment, since the twist angles of the liquid crystal molecules in the first and second cell layers are substantially the same, the product of the birefringence (Δn) and the thickness (d) of the liquid crystal layer in each of the first and second cell layers (Δn · d ) Are almost identical to each other.

In a preferred embodiment, since the torsion angles of the liquid crystal molecules in the first and second cell layers are substantially equal to each other, the birefringence (Δn ₁ ) and the thickness of one of the liquid crystal layers of the first and second cell layers subjected to optical changes by an external force. The product of (d ₁ ) (Δn ₁ · d ₁ ) and the product of the birefringence (Δn ₂ ) and thickness (d ₂ ) of the liquid crystal layer in another cell layer that are not subjected to optical change (Δn ₂ · d ₂ ) are Indicates.

Δn ₂ , d ₂ <0.85Δn ₁ , d ₁

In a preferred embodiment, the twist angle of the liquid crystal molecules in each of the first and second cell layers is in the range of 180 ° to 360 °.

In a preferred embodiment, the relationship between the torsion pitch p of the liquid crystal molecules in the cell layer with the voltage application means and the thickness d of the liquid crystal layer in the cell layer is as follows:

θ/2πθ / 2π-1 / 4 <d / p

θ / 2π

Is the torsion angle of the liquid crystal molecules.

In a preferred embodiment, the color filter layer is disposed on at least one of the first and second cell layers.

In a preferred embodiment, an active element is disposed in each image element in at least one of the first and second cell layers.

Accordingly, the present invention provides a liquid crystal display device that (1) produces a colored display image with very good color reproducibility and high contrast, and (2) a liquid crystal display device that obtains a full-color display or a multi-color display. To make it possible.

The present invention will be better understood by those skilled in the art for the purpose and advantages thereof based on the accompanying drawings.

The present invention provides a liquid crystal display device, wherein the basic structure of the double-layer cell of the device includes a first cell layer C ₁ and a second cell layer (C ₁ ) containing liquid crystal molecules in a torsional nematic orientation as shown in FIG. C ₂ ). Each cell layer is formed of a transparent substrate 1 such as glass or acrylic resin, a transparent conductive film 2 such as ITO or Nesa film on the substrate 1, a liquid crystal molecule located on the substrate 1 and the transparent conductive film 2, and the like. Polarizer 5 located on the back of the substrate 1 and the alignment film 3 such as an inorganic film made of SiO ₂ , SiO or the like or an organic film made of polyimide, polyvinyl alcohol, nylon, acrylic resin, etc. It is composed. Both ends of each cell layer are sealed with a sealing water ring (6). The liquid crystal layer 4 is disposed in each cell layer C ₁ and C ₂ .

The helical twisting direction of the liquid crystal molecules of the liquid crystal layer 4 in one cell layer is opposite to the direction of the molecules of the liquid crystal layer 4 in the other cell layer. The twisting direction of the liquid crystal molecules is set as shown in FIGS. 2A and 2B, where FIG. 2A shows the twisting of the liquid crystal molecules in the right direction with respect to the direction in which light from the light source is projected onto the cell, and FIG. Fig. 1 shows the twisting of the liquid crystal molecules in the left direction with respect to the light transmission direction. When an optically active material is added to the nematic liquid crystal, the liquid crystal molecules form a torsion structure. In order to induce the twist in the right direction to the liquid crystal molecules, a material represented by the following chemical structure is used as the optically active material.

In order to induce the twist in the left direction to the liquid crystal molecules, cholesteryl nonanoate (Merck), S-811 (Merck) and the like are used as the optically active material.

Further, the torsion angles θ ₁ and θ ₂ of the liquid crystal molecules of the liquid crystal layers in the first and second cell layers are set in the optimum range. The values of Δn ₁ · d ₁ and Δn ₂ · d ₂ of the liquid crystal layers in the first and second cell layers (Δn ₁ and Δn ₂ are birefringence of the liquid crystals in the first and second cell layers, respectively, and d ₁ and d ₂ is the thickness of the liquid crystal layer in the first and second cell layers, respectively). The optimum ranges of the torsion angles θ ₁ and θ ₂ and Δn ₁ · d ₁ and Δn · d ₂ values of the liquid crystal molecules described above are set in consideration of the following three requirements.

(1) FIG. 3 shows the difference between the values of Δn ₁ · d ₁ and Δn ₂ · d ₂ and the transmittance when θ ₁ and θ ₂ are set to 90 ° and arranged in a cross-nicotine manner with no voltage applied. Indicates a relationship. 3 shows that when the Δn ₁ · d ₁ value of the first cell layer is the same as the Δn ₂ · d ₂ value of the second cell layer, the transmittance becomes the lowest, and a high contrast ratio can be obtained. This phenomenon occurs because the light dispersion in the first cell layer is compensated by the second cell layer. The above results can be obtained not only when the twist angles θ ₁ and θ ₂ are set to 90 °, but also when the angles are set to any angle. Further, even if the torsional intrinsic pitch of the liquid crystal molecules in the first cell layer is different from the torsional intrinsic pitch of the liquid crystal molecules in the second cell layer, the same result as described above can be obtained when the torsion structure has a preferable torsion angle of the liquid crystal molecules.

In addition, as shown in FIG. 4, it is preferable to set the twist angle of the liquid crystal molecules in the range of about 180 ° to about 360 ° based on the relationship between the twist angle and the contrast ratio in consideration of display contrast and visibility. When the torsion angle of the liquid crystal molecules exceeds 360 °, an area in which the liquid crystal has a disordered orientation upon application of voltage is generated and light is dispersed, thereby easily reducing the contrast.

(2) In order to obtain an accurate threshold value of contrast, the twist intrinsic pitch p of the liquid crystal molecules of one cell layer having an application means is very important. The ratio of the thickness d of the liquid crystal layer to the torsion pitch p of the liquid crystal molecules, i.e., d / p, is preferably set using experimental data as follows.

θ/2πθ / 2π-1 / 4 <d / p

θ / 2π

Is the torsion angle of the liquid crystal molecules. This requirement works when the pretilt angle of the liquid crystal is about 10 degrees or less. The above requirement is used in the general cross display system in which the liquid crystal shows white color upon application of voltage.

(3) The following third requirement is used in a general whitening display system.

For example, the product (Δn ₁ · d ₁ ) of the birefringence (Δn ₁ ) and the thickness (d ₁ ) of the liquid crystal layer in the first cell layer is 0.7 (ie, Δn ₁ · d ₁ = 0.7), and the second cell layer The product of the birefringence (Δn ₂ ) and the thickness (d ₂ ) of the liquid crystal layer (Δn ₂ · d ₂ ) is 0.5 (ie, Δn ₂ · d ₂ = 0.5), and in each of the first and second cell layers When the twist angle of the liquid crystal molecules is 270 °, the transmittance is about 70% when the applied voltage is zero. As shown in Fig. 5, the transmittance is drastically reduced by applying a voltage to the first cell layer. This is because the application of voltage pulls up the liquid crystal molecules in the first cell layer and apparently decreases Δn ₁ · d ₁ of the liquid crystal layer in the first cell layer, so that Δn ₁ · d ₁ is the Δn of the liquid crystal layer in the second cell layer. _2, because it is the same as d _2.

In order to obtain this phenomenon, Δn ₂ · d ₂ must be smaller than Δn ₁ · d ₁ . When the value of Δn ₂ · d ₂ approaches the Δn ₁ · d ₁ value remarkably, as shown in FIG. 3, the transmittance is significantly lowered when the applied voltage is zero. Therefore, Δn ₂ · d ₂ must conform to the following inequality:

Δn ₂ , d ₂ <0.85Δn ₁ , d ₁

Moreover, the requirements for the preferred twist angle and the desired d / p ratio of the liquid crystal molecules are the same as the requirements for the twist angle and the d / p ratio in the case of the general cross-display method. Furthermore, in order to obtain a state in which the liquid crystal layer becomes white, the thickness of the liquid crystal layer is preferably set to about 10 占 퐉 or less when θ is 180 ° ≤θ≤360 °.

Example 1

6 shows a _two- layer cell structure (ie, two-layer TN-LCD) of the liquid crystal display device of the present invention, wherein the twist angle of the liquid crystal molecules in each of the first and second cell layers C ₁ and C ₂ is 90 °. It is shown. By depositing ITO, a transparent conductive film 12 is provided on each glass substrate 13 of only the first cell layer C ₁ . On the glass substrate 13 and the transparent conductive film 12, a liquid crystal-molecule alignment film 16 of polyimide was applied to a thickness of about 1000 mm by a rotation coating method, and the surface thereof was rubbed with a cloth to twist the liquid crystal molecules. (TN) Orientation. The end of the cell layer is sealed by the sealing material 14. Nematic liquid crystal ZLI-3281 (MERCK) is used as the liquid crystal material. The first cell layer will be 0.5% by weight of the cholesteryl no nano-benzoate to the liquid crystal layer 15 of the (C ₁₎ added, and the addition, 0.15% by weight of the second CB15 to the liquid crystal layer 15 of the cell layer (C _2). The twist angle of the liquid crystal molecules in the _first cell layer C ₁ opposes the twist angle of the liquid crystal molecules in the _second cell layer C ₂ . The thickness of each of the liquid crystal layers of the first and second cell layers C ₁ and C ₂ (that is, the thickness of each cell layer C ₁ and C ₂ ) is about 5 μm. The polarizer 11 is installed in a cross-nicole method.

7A and 7B show the dependence of the light transmittance on the applied voltage in the two-layer TN-LCD and the reference single-layer TN-LCD of the present invention, wherein the wavelength λ used here is for red. 610 nm, 550 nm for green and 450 nm for blue, and when voltages below the threshold are applied, the transmittances of the respective wavelengths for red and blue in the bilayer cell are determined for red and blue in the monolayer cell. It shows that the transmittance | permeability of each wavelength is lower. This means that the bilayer cell can obtain high contrast. Moreover, the dependence of the applied voltage-transmission characteristic on the wavelength in the double-layer cell is much smaller than the dependence of the applied voltage-transmission characteristic on the wavelength in the monolayer cell, so when the full-color display is performed, Can produce a display image with much better color reproducibility.

Example 2

8 shows another liquid crystal display device (ie, two-layer type) in which the twist angle of each liquid crystal molecule of the first and second cell layers C ₁ and C ₂ is 270 ° (that is, the liquid crystal molecules are super twisted). SBE). By depositing ITO, a transparent conductive film 22 is provided on each glass substrate 23 of only the first cell layer C ₁ . On the glass substrate 23 and the transparent conductive film 22, a liquid crystal-molecule alignment film 26 of polyimide was applied to a thickness of about 1000 mm by a rotation coating method, and the surface thereof was rubbed with a cloth to treat the vertical axis of the liquid crystal molecules. The liquid crystal molecules are aligned so as to be parallel to the substrate. The end of the cell layer is sealed by a sealing material 24.

Nematic liquid crystal ZLI-3281 (MERCK) is used as the liquid crystal material. The first cell layer will be 1.1% by weight of the cholesteryl no nano-benzoate to the liquid crystal layer 25 of the (C ₁₎ added, and the addition, 0.94% by weight of a second cell layer CB15 to the liquid crystal layer 25 of the (C _2).

The torsion pitch of the liquid crystal molecules is about 8 mu m, and the pretilt angle of the liquid crystal molecules placed on the substrate is 8 degrees.

The twist angle of the liquid crystal molecules in the _first cell layer C ₁ opposes the twist angle of the liquid crystal molecules in the _second cell layer C ₂ . The thickness of the liquid crystal layer (ie, the thickness of each cell layer C ₁ , C ₂ ) of each of the first and second cell layers C ₁ , C ₂ is about 5 μm. The polarizer 21 is provided as shown in FIG. 1 in a cross-nicole manner.

FIG. 9b shows the dependence of the light transmittance on the applied voltage in the double-layer SBE of the present invention, and FIG. 9a shows the same characteristics as the above for the standard single-layer SBE for control, and the wavelength? Is 610 nm for red, 550 nm for green and 450 nm for blue. 9A and 9B show that the transmittance of each wavelength in the bilayer cell is lower than the transmittance of each wavelength in the monolayer cell when the voltage is applied below the threshold value. Moreover, the bilayer cell has a unique and sharp threshold characteristic for the SBE cell such that the cell can produce a display image with high contrast at high impact driving.

Moreover, since the dependence of the applied voltage-transmission characteristic on the wavelength in the bilayer cell is smaller than the dependence of the applied voltage-transmission characteristic on the wavelength in the monolayer cell, the bilayer cell is useful for color display. Do.

Example 3

FIG. 10 shows another liquid crystal display device of the present invention (i.e., two-layer SBE) in which the twist angles of the liquid crystal molecules of the first and second cell layers C ₁ and C ₂ are 270 ° (i.e., the molecules are super twisted). It is shown. The value of Δn ₁ · d ₁ of the first cell layer C ₁ and the value of Δn ₂ · d ₂ of the second cell layer C ₂ are adjusted to 0.7 and 0.5 by varying the thickness of the cell layer. The cell structure of this display device is the same as that of the second embodiment except that the display device has an electrode 32 for voltage application of the first cell layer C ₁ . FIG. 11B shows the dependence of the light transmittance on the applied voltage in the double-layer SBE of the present invention. FIG. 11A is the same as that of FIG. 11B in the reference single-layer SBE having a torsion angle of 270 ° for the liquid crystal molecules of the monolayer cell. Features are shown. 11a and 11b show that the bilayer cell is special for SBE cells, has sharp characteristics as well, and that the characteristic change of the double layer cell at red, green, and blue wavelengths is much smaller than that of the single layer cell. This can be seen at Thus, the double-layer cell can obtain a color display image with high contrast.

Example 4

A color (red, green and blue) filter layer of a gelatin film is provided inside the liquid crystal cell layer having the voltage application means of each display device in the above embodiment. A display device having a color filter layer performs impact driving with the formation of a clear and clear color image.

These liquid crystal display devices are useful for full-color displays and multi-color displays.

Example 5

The liquid crystal cell of the present invention is used in place of a liquid crystal panel having a TFT (Thin Film Transistor) color filter as an active element, and a color display test is conducted by active matrix driving. Since they produce clear and sharp color images, they are useful for full-color displays and multi-color displays.

It will be apparent to those skilled in the art that the present invention can be variously modified without departing from the scope of the present invention. Accordingly, the claims appended hereto are not intended to limit the content described herein, but are inherent in the present invention, including all features that may be treated as equivalents thereof by those skilled in the art. It should be noted that the claims are set forth inclusive of the patentable novelty features.

Claims (3)

A two-layer liquid crystal cell composed of a first cell layer and a second cell layer containing liquid crystal molecules having a torsional nematic orientation, and a voltage applying means in one of the first and second cell layers, and the liquid crystal molecules in the first cell layer The torsion angle of is opposite to the torsion angle of the liquid crystal molecules in the second cell layer, and the torsion angles of the liquid crystal molecules of each of the first and second cell layers are 180 ° to 360 °, and the liquid crystal molecules in the first cell layer near the second cell layer. Is orthogonal to the orientation of the liquid crystal molecules in the second cell layer near the first cell layer, and the product of birefringence and thickness of each of the first and second cell layers is represented by the following inequality, Δn ₂ , d ₂ <0.85Δn ₁ , d ₁ A relationship between the pitch (P) of twisting of liquid crystal molecules in a cell layer having a voltage applying means and the thickness (d) of the liquid crystal layer in the cell layer is as follows. θ / 2π-1 / 4 <d / p

θ2 / π Where θ is the torsion angle of the liquid crystal molecules The liquid crystal display device according to claim 1, wherein a color filter layer is provided on at least one of the first and second cell layers. 2. The liquid crystal display device according to claim 1, wherein an active element is provided on each image element in at least one of said first and second cell layers.

Images